Maybe you could branch out a bit and find a subreddit that's writing related, or just related to some topic in your novel I've also heard good things about Facebook groups and Google+. You could also create your own Facebook group (or even a simple blog, using a site like Squarespace or Wix) and start posting relevant and useful content there - like writing advice, how you created your characters, etc. It's always good to have your own site where people can consume your stuff. I've just started to work on my comic but I will eventually (after a few chapters and more interest) create a site and a place for my stuff to live online that I control.
You have to give people ways to find you and if you have a site that has relatively good SEO (search engine optimization - so, lots of word-heavy content like blogs and articles), it increases your chances of getting found on Google and other search engines.
You can use the same approach on a platform like Pinterest - create boards that are relevant to what others might like. A fan art board, a meme board, an inspirational quote board.
As a follow-up to that kind of content on Pinterest, you might also try to commission art (if you're not good at it yourself) of your characters. Make sure it's sleek and polished. Look at some ads on Pinterest (they're called promoted pins) and see what catches your eye. Throw an eye-catching, intriguing line of copy on there (can be a quote by one of your characters, or a snippet of a review someone left about your novel), turn that into a pin (a post on Pinterest) and then link that to wherever your novel is. Pinterest is phenomenal because the return on your original post is great...It has a very broad reach.
Think of your novel as a product. When you see marketing for movies,shows, books, what do you see? It's pieces of the story that will resonate with people. Trailers, quotes, posters, memes. Create a meme from your novel and share it on Tumblr!
I work in ecommerce marketing so I know some basic things about online marketing. I know it's not totally relevant to what we're doing here but hopefully some of that will help! Sometimes, posting on social media can feel like you're shouting out into the void. You have to find your target audience (the people you want to read your story, who are genuinely interested in what you do) and engage with them.
[EDIT]
Also, I recently discovered something called Amino Apps which markets itself as "network of communities [that] lets you explore, discover, and obsess over the things you're into." Kinda like a Twitter+Reddit combined. Definitely gonna check that out, it sounds like the perfect way to find a community that's into your stuff. You can also create your own "Amino" on there, so basically a little fan community for your novel. It's great!
[EDIT EDIT]
Your topic inspired me to create a thread about marketing your creative work - check it out, if you like! I hope it becomes a place where people can continuously bounce ideas off each other on how to market themselves. If it takes off, you might find some more useful info there